Talk:How to setup boot loaders

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Revision as of 10:46, 27 November 2005 by 194.166.240.76 (Talk) (→‎Interferences with BIOS)
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Why does the article say that LILO/GRUB occopy the "MBR or boot sector" while NT Boot Loaded occupies both? You can boot Windows with a GRUB MBR or GRUB with a Windows MBR, so I don't see why the latter is true.
(BTW, sory for the misflag, last edit wasn't "minor".)

--Thinker 09:10, 1 Oct 2005 (CEST)

There might be a better expression for that. What it should say is that NTLDR will always install to the partitions boot sector. You can't just install NTLDR to the MBR (as you can do with grub and lilo). Since it installs to the boot sector, you will also have to install something into the MBR that runs that boot sector. If you just install Windows that boot code kind of also belongs to the NT boot loader. Hence, to have an NT boot loader running, you need to have boot code in both the MBR and the boot sector. Wyrfel 14:13, 1 Oct 2005 (CEST)

Interferences with BIOS

When I got a new PC (Gericom Phantom 31100 with AMD Sempron) the first thing was to add Linux to the preinstalled Windows XP.

Here what happended to me: Booting from Linux install disk and starting installation: Everything fine but what I didnt know: Geometry as reported from disk was different to geometry on disk. The Windows XP somehow assumed that number of heads is 255 while the disk reported 63. Additionally the BIOS reported "LBA off" (AMI-Bios 8.00.12 allows only [AUTO] for hard disk recognition and I found no chance to set that using BIOS menu).

The result: Neither Linux nor Windows was anymore bootable, Windows not even from Recoverty Disk !!!!. By bad luck I even lost the original MBR in my helpless attempts to fix that using different bootloader configurations. The best I could archieve: Using the force-lba option in GRUB made the stage 1 loadable but not stage 2. And asking for help thru helpline of manufacturer: No answer till today (3 weeks from now).

But I found some hints on Linux pages about: Windows takes number of heads from partition table and refuses to boot in that case. So a applied the suggested fix 

> sfdisk -d /dev/hda | sfdisk --no-reread -H255 /dev/hda

Warning: HDIO_GETGEO says that there are 16 heads

Disk /dev/hda: 193821 cylinders, 255 heads, 63 sectors/track
Old situation:
Warning: The partition table looks like it was made
  for C/H/S=*/16/63 (instead of 193821/255/63).
For this listing I'll assume that geometry.
Units = cylinders of 516096 bytes, blocks of 1024 bytes, counting from 0

   Device Boot Start     End   #cyls    #blocks   Id  System
/dev/hda1   *      0+  79191   79192-  39912736+   7  HPFS/NTFS
/dev/hda2      79192   81271    2080    1048320   82  Linux swap
/dev/hda3      81272  193820  112549   56724696   83  Linux
/dev/hda4          0       -       0          0    0  Empty
New situation:
Units = sectors of 512 bytes, counting from 0 

   Device Boot    Start       End   #sectors  Id  System
/dev/hda1   *        63  79825535   79825473   7  HPFS/NTFS
/dev/hda2      79825536  81922175    2096640  82  Linux swap
/dev/hda3      81922176 195371567  113449392  83  Linux
/dev/hda4             0         -          0   0  Empty
Warning: partition 1 does not end at a cylinder boundary

sfdisk: I don't like these partitions - nothing changed.
(If you really want this, use the --force option.)

and using --force made me happy: Both, Linux and Windows now bootable.

Summary: There a propably 4 problem areas / errors

1) BIOS tells lba=off for a ATA disk which has LBA=yes after autodedect In my opinion a bios error

2) grub-install produces (and overwrites) an MBR which is based on what the disk reports and not on original partition table

3) Windows XP boot terminated when a completly unnecessary check (number of heads when using LBA) fails

4) grub doesnt pass thru the force-lba to stage 2

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